Alloy steels



United States Patent 3,117,863 ALLOY STEELS George A. Roberts and John C. Hamaker, In, Latrobe, Pa, assignors to Vanadium-Alloys Steel Company, Latrobe, Pa, a corporation of Pennsylvania No Drawing. Filed Nov. 14, 1960, Ser. No. 68,692 12 Claims. (Cl. 75-126) This invention relates to a new class of steels and to a new method of making such steels.

This application is a continuation-in-part of our copending application Serial No. 776,271, filed October 29, 1958, now abandoned, entitled Alloy Steels, and the disclosure of the latter application is incorporated herein and made a part hereof by reference as fully as if it were set forth herein as such.

Under the microscope, hardened high speed steel is found to consist essentially of two phases; extremely hard excess alloy carbides and a matrix or background material. This aggregate of excess carbides and matrix material provides probably the highest stren th properties currently available in any material as evidenced by the articles entitled, The Bend Test for Hardened High Speed Steel, by Arthur H. Grobe and George A. Roberts, Transactions of the American Society for Metals, vol. 40, 1948, pp. 435-490, and Bend: Tensile Relationships for Tool Steels at High Strength Levels, by John C. Hamaker, In, Vance C. Strang, and George A. Roberts, Transactions of the American Society for Metals, vol. 49, 1957, pp. 550575. High speed steels while possessing high strength properties suffer from the disadvantage of being brittle. Ultra-high strength structural steels, on the other hand, are tough and ductile but are not as strong as the high speed steels. Steels with the strength of high speed steels and the toughness and ductility of ultra-high strength steels will therefore fill a long felt need in the art.

In view of the foregoing an object of our invention is to provide a new family or class of steels of this nature, characterized by the fact that they have the same approximate hardness of high speed steel and the same approximate toughness and ductility of ultrahigh strength steels.

Another object of our invention is to provide a new method of making such steels according to which the desired degrees of hardness, toughness and ductility may be conveniently and economically produced.

Other objects and many of the attendant advantages of our invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying tables.

For many years, various academic studies have been conducted to determine the composition of high speed steels. The work of Grossman and Bain is summarized in their book High Speed Steel, copyright 1931, by John Wiley and Sons. Other recent studies are summarized in the following paper: The Effect of Vanadium and Carhon on the Constitution of High Speed Steel, by Donald J. Blickwede, Morris Cohen and George A. Roberts, Transactions of the American Society for Metals, vol. 42, 1950, pp. 1161-1196. With the improved methods of determining the excess carbide analysis and content in high speed steels, the matrix compositions can be determined vvith acceptable accuracy, thus opening a new area for research and development.

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We have discovered that new steels having compositions which correspond to the compositions of the matrices of heat treated high speed steels may be heat treated to produce a new class of steels having the same approximate toughness and ductility of ultra-high strength steels and approaching the strength of high speed steel.

When proceeding according to our invention, a heat treated high speed steel is preselected which has the strength characteristics that are desired in our finished structural composition. The high speed steels alluded to in this application are described as steels having essentially martensi-tic matrices, with room temperature hardness of about Rockwell C and above, hot hardness of about Rockwell C 45 and above at about 0 F. and which contain more than about 5% undissolved excess carbides. These high speed steels are usually hardened at temperatures above 2000 F. when processed. Owing to the inclusion of excess carbides throughout the structure of the high speed steels, the preselected steel is generally too brittle for structural use. The matrix composition of the preselected high speed steel is determined by the analytical methods referred to above and a new melt is prepared, the chemical analysis of which corresponds to the matrix composition of the parent high speed steel. The composition is preferably made by a vacuum melting method although it is possible to employ air melting methods presently used in the industry. Of the Vacuum melting methods available, applicants prefer to make the composition by the consumable electrode vacuum melting technique.

The chemical analysis of our steel is such that essentially all of the carbides which are customarily present in excess quantities in the annealed or softened parent steel, will be dissolved in our steel when the latter is heated for hardening. The resulting steel throughout closely resembles the matrix of the parent steel in structure without the inclusion of excess carbides. Ingots of our new steel are then cast and the steel is processed and heat treated in accordance with the normal specifications of the preselected parent high speed steel. The steel thus produced is more ductile and tougher than the parent steel and yet possesses higher hardness than normal structural steels. However, the absence of excess carbides permits grain boundary movement during heat treatment which results in grain coarsening. To obtain a fine grain size essential to maximum toughness and ductility in the new composition, the hardening temperature should be lowered about F or alternatively, to a point where a slight amount of excess carbide is produced for restricting grain growth. In any event the lower hardening temperature selected is such that less than 5% undissolved excess carbides are present in the hardened essentially martensitic matrix. Thus we obtain a new composition which closely resembles the matrix of the preselected high speed steel, yet is considerably tougher and more ductile at substantially high hardness levels.

Listed below are eight high speed steel compositions which fall within ranges of eight high speed steels commerically available, together with their corresponding matrix compositions. It should be understood that the compositions listed below are typical examples of innumerable compositions falling within the scope of the invention and the invention is not to be construed as limited to the specific compositions about to be discussed since there are several dozen high speed steels commer- EXAMPLE I Nominal composition of high speed steel A:

.70% carbon 18.00% tungsten 4.00% chromium 1.00% vanadium and the remainder substantially iron Nominal matrix composition of high speed steel A:

.5 carbon 8.6% tungsten 4.4% chromium 1.00% vanadium and the remainder substantially iron EXAMPLE II Nominal composition of high speed steel 33:

.80% carbon 18.00% tungsten 4.00% chromium 2.00% vanadium and the remainder substantially iron Nominal matrix composition of high speed steel B:

.5 carbon 8.0% tungsten 4.4% chromium 1.7% vanadium and the remainder substantially iron EXAMPLE III Nominal composition of high speed steel C:

.75% carbon 18.00% tungsten 4.00% chromium 1.00% vanadium 5.00% cobalt and the remainder substantially iron Nominal matrix composition of high speed steel C:

.4% carbon 8.3% tungsten 4.7% chromium 1.1% vanadium 5.6% cobalt and the remainder substantially iron EXAMPLE IV Nominal composition of high speed steel D:

1.50% carbon 12.00% tungsten 4.00% chromium 5.00% vanadium 5.00% cobalt and the remainder substantially iron Nominal matrix composition of high speed steel D:

.4% carbon 7.3% tungsten 5.1% chromium 1.4% vanadium 4.3% cobalt and the remainder substantially iron EXAMPLE V Nominal composition of high speed steel E:

.80% carbon 1.50% tungsten 8.00% molybdenum 4.00% chromium 1.00% vanadium and the remainder substantially iron Nominal matrix composition of high speed steel E:

.6% carbon .9% tungsten 4.7% molybdenum 5 3.9% chromium .9% vanadium and the remainder substantially iron EXAMPLE VI Nominal composition of high speed steel F:

.80% carbon 6.00% tungsten 5.00% molybdenum 4.00% chromium 1a 2.00% vanadium and the remainder substantially iron Nominal matrix composition of high speed steel F:

.5% carbon 2.0% tungsten 3.0% molybdenum 4.6% chromium 1.0% vanadium and the remainder substantially iron EXAMPLE v11 Nominal composition of high speed steel G:

1.30% carbon 5.50% tungsten 4.50% molybdenum 4.00% chromium 4.00% vanadium and the remainder substantially iron Nominal matr'm composition of high speed steel G:

.5 carbon 3.5% tungsten 3.2% molybdenum 4.7% chromium 40 1.9% vanadium and the remainder substantially iron EXAMPLE VIII Nominal composition of high speed steel H: .85 carbon 8.00% molybdenum 4.00% chromium 2.00% vanadium and the remainder substantially iron Nominal matrix composition of high speed steel H:

.5 carbon 5.4% molybdenum 4.2% chromium 1.1% vanadium and the remainder substantially iron The nominal analysis of the compositions, which correspond to the matrix composition of the parent steel may vary :l% for nominal contents of 5% or greater, i.5% for nominal contents of from 1% to 5%, and 1.25% for nominal contents of other elements, such as silicon and manganese, which are present in quantities of less than 1.0%. Such variations lie within the 6 contemplation of the invention. In general the carbon content for the new class of steels generally varies from .20 to .80% for the entire class while remaining within the scope of the invention. Once the matrix composition of a parent high speed steel is determined, it will 7 serve as a target for the production of our compositions which may vary somewhat during processing, as indicated.

To demonstrate the results obtained when proceeding according to our invention, a detailed discussion of the properties; treatment and composition of a typical steel will now be given. The matrix of the steel under consideration has the following composition:

This is a more complete analysis of the matrix of steel F set forth in Example 6, above, and includes the percentages of silicon, manganese, sulfur and phosphorous contained therein. The parent high speed steel of which it is the matrix composition bears the Standard AISI designation of M-2 and includes all compositions within the following commercial range:

.80 to .85% carbon .20 to .40% silicon 6 Temperature for preheating, 1400 to 1500 F. Austenitizing temperatures, 2150 to 2250 F., recommended, 2225 F. Tempering temperature, 1000 to 1150 F.

A melt was made of a composition corresponding to the detailed matrix composition of high speed steel F. This melt was cast into a 7", 300 pound ingot. The ingot was then forged at the same temperatures (2050 to 1700 F.) as the parent high speed steel (Vasco M2) is customarily forged, and rolled. In rolling, the matrix steel was treated like a hot Work die steel and no dlfi'lCLlltlBS were encountered. A n" bar, 10 feet long was selected and subjected to high speed annealing, at about 1625 F. From this annealed stock, cubes were selected and preheated at a temperature 1500 F. The samples were austenitized in a gas-fired, semimuffle type furnace for five minutes at various temperatures and oil quenched or air cooled. The as quenched hardness and intercept grain results for both oil quenched and air cooled samples from various temperatures, together with the hardness figures after each tempering at 1000 F. for two hours, are set forth in Table I below.

Table l ROCKWELL HARDNESS AVERAGES FROM SIX READINGS Austenit; Austenit- Air cooled Oil Quenched Intercept Grain Size izrng izing Tempera- Time,

tnre, Minutes As First Second Third As First Second Third Oil Air F. Quenched Temper Temper Temper Quenched Temper Temper Temper Quenched Cooled 5 54. 3 53. 4 54. 52.9 55.6 51. 3 52. 6 52.1 53. 0 56. 0 56. 5 56. 6 60.2 55. 7 55.9 55. 9 5 61. 0 57. 3 5s. 9 59. 4 62. 7 59. 5 67. 5 59. 5 5 62. 2 60.7 51. 5 60.9 63.1 60.1 60.3 60.2 5 62. 7 61. 6 61. s 61. 2 62. 4 60.5 61. 1 61.2 62. 7 61.7 61.3 61.3 62. 9 60.5 59. s 61.0 5 62. 3 60.3 61.3 61.8 62. 2 61.2 60.9 61. 2 62. 0 60.3 61.6 61. 7 62. 6 60. 3 60. 4 61. 0

.20 to .30% manganese Austenitizing temperatures of 2050 F. (175 below 03% maximum sulfur that recommended for the parent high speed steel) and 03% maximum phosphorous 2225 F. (that recommended for the parent steel) were 6.00 to 6.75% tungsten selected for further tempering study and comparison and 3.90 to 4.40% chromium the austenitizing procedure employed for the as-quenched 1.75 to 2.05% vanadium hardness samples was kept the same. All samples were 4.75 to 5.25% molybdenum oil quenched from the two austenitizing temperatures and and 318 Ifimfimdef substantlany Iron G the intercept grain size values were 11.7 at 2050 F. and

This parent high speed steel has a Wide hardening range and is a high speed steel having relatively high ductility at high hardness levels. In general, the com- 2.8 at 2225 F. Rockwell C hardness readings were taken after each tempering cycle for the various tempering temperatures, and are listed below in Table II.

Table II ROCKWELL HARDNESS MEASURED AFTER EACH OF THREE TWO-HOUR TEMPERS Austenitized 2,050 F. Austenitized 2,225 F. Tampering Temperature As First Second Th1rd As First Second Th1rd Quenched Temper Temper Temper Quenched Temper Temper Temper position is usually heat treated in accordance with the In addition, .505" round specimens were prepared and following schedule, to obtain normal hardness from anstenitized at 2050 F. and 2225 F., respectively, for to Rockwell C: five minutes, air cooled and triple tempered 2+2+2 'pemperamre f f i 2950 to 1700 F hours. The room temperature tenslle properties are set forth below 1n lable III.

Temperature for annealing, 1550 to 1600 F.

Table I I I Yield Strength, p.s.i. True Tensile Elonga- Red. in Fracture Tcmpering Tempera- Hardness, Strength, tion in Area, Stress,

ture, F. Re Prop. 0.01% 0.02% 0.1% 0.2% p.s.i. 4D, Percent p.s.i.

Limit Ofiset Otisct Ollsct Otiset Percent Ar stenitized at 2,050

1 Fractured in threads.

From the room temperature tensile properties recorded in Table Ill, it should be noted that the austenitizing temperature of 2050 F. produces a matrix steel with much better ductility than the standard hardening temperature of 2225 F. for the parent high speed steel.

The comparative hardness figures for standard Vasco M-2 and our matrix composition are summarized in Table IV below and indicate the small hardness difierentials of the two steels hardened from 2225 F. and tempered for 2 hours at the designated temperatures.

Table IV Tempered Hardness (2 hours) He Tempering 'li ernperature,

. Vasco M-2 Matrix Composition As quenched 64. 7 63. 2 5 60.6 57.2 61.5 58.0 62.5 00.0 64.4 61.0 65.8 61.8 65.1 60.8 64.0 59.1 1,150 62. 7 55. 5 1,200-- 59. 3 52. 3 1,300 46. 1 40. 0

In Table V below, our matrix composition is compared with standard Vasco M-2 high sped steel and H-ll, an ultra-high strength steel.

Table V Unnotched Izod Impact V-Notch Charpy Impact Strength, t.-1bs. Strength, ft.-lbs. Heat Treated Hardness, Standard Matrix Matrix Matrix AISI H-ll Re M2 High M2 Aus- M2 Aus- M2 Aus- Hot Work Speed tenitized tenitized tenitized Die and Steel at 2225F. at 2050F. at 2050F. Structural Steel 'The comparative toughness of our matrix steel as shown in Table V, reveals the unique properties of our material. Using the unnotched Izod impact test, we find that the toughness of matrix M2, austenit-ized at the lower hardening temperature, exceeds the capacity of the machine (greater than 120 ft.-lbs.). A number of specimens were tested using another hammer position normally used for Charpy testing, which delivers 264 ft.-lbs. of energy, and fracture was resisted in most cases. In view of the toughness of our matrix composition, additional specimens were tested using the standard V-notch Charpy method. These results comparing the matrix steel with the ultra-high strength structural steel, are set forth in the last two columns. Since the ultra-high strength steels are limited to a maximum hardness of about 57 Rockwell C further comparisons could not be made at the higher hardness levels.

In conclusion, it is theorized that our new matrix steels fill -:a gap between the ultra-high structural steels, which are limited to about 57 Rockwell C hardness and the very strong but brittle standard high speed steels which can he heat treated to Rockwell C or greater. In this sense our new class of steels may be regarded as intermediate high strength and high speed steels, which possess room temperature hardness ranging from in excess of Rockwell C 57 and up to about Rockwell C 62, while possessing high ductility after austenitizing and tempering. From the test results in Table V, the high ductility of our new class of steels at high hardness levels, is best characterized by an unnotched impact to hardness factor in excess of 2 ft. lbs/Rockwell C.

It will be seen that the objects set forth above, among those made apparent from the preceding description are eificiently attained and, since certain changes may be made in the compositions and in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description and set forth in the accompanying tables shall be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, what we claim and desire to protect by Letters Patent of the United States is:

1. A method of making a new alloy steel comprising the steps of, determining the chemical composition of the essentially martensitic matrix of a hardened high speed steel, the high speed steel having a composition of chromium+tungsten+vanadium+2 times the molybdenum of at least about 21%, a room temperature hardness of about Rockwell C 60 and above, a hot hardness of about Rockwell C 45 and above at about 1000 F. and more than about 5% undissolved excess carbides, preparing a composition corresponding approximately to the chemical composition of the essentially martensitic matrix within the following limits, 11% for compositional elements with nominal contents of 5% or greater, i.5% for compositional elements with nominal contents of from 1 to 5%, :.25% for compositional elements'with nominal contents of 1% or less, and with the carbon content ranging from about 20% to about .80%, and hardening the prepared composition at substantially the same hardening temperature employed for hardening the high speed steel.

2. The method of claim 1 further defined in that said matrix composition is hardened at a lower hardening temperature so that undissolved excess carbides are formed, said lower hardening temperature being such that less than 5% undissoilved excess carbides are formed.

3. A method of making anew alloy steel afiter determining and preparing a chemical composition corresponding approximately to the chemical composition of the 

1. A METHOD OF MAKING A NEW ALLOY STEEL COMPRISING THE STEPS OF, DETERMINING THE CHEMICAL COMPOSITION OF THE ESSENTIALLY MARTENSITIC MATRIX OF A HARDENED HIGH SPEED STEEL, THE HIGH SPEED HAVING A COMPOSITION OF CHROMIUM+TUNGSTEN+VANADIUM+2 TIMES THE MOLYBDENUM OF AT LEAST ABOUT 21%, A ROOM TEMPERATURE HARDENESS OF ABOUT ROCKWELL "C" 60 AND ABOVE, A HOT HARDENESS OF ABOUT ROCKWELL "C" 45 AND ABOVE AT ABOUT 1000*F. AND MORE THAN ABOUT 5% UNDISSOLVED EXCESS CARBIDES, PREPARING A COMPOSITION CORRESPONDING APPROXIMATELY TO THE CHEMICAL COMPOSITION OF THE ESSENTIALLY MARTENSITIC MATRIX WITHIN THE FOLLOWING LIMITS, $1% FOR COMPOSITIONAL ELEMENTS WITH NOMINAL CONTENTS OF 5% OR GREATER, $.5% FOR COMPOSITIONAL ELEMENTS WITH NOMINAL CONTENTS OF FROM 1 TO 5%, $.25% FOR COMPOSITIONAL ELEMENTS WITH NOMINAL CONTENTS OF 1% OR LESS, AND WITH THE CARBON CONTENT RANGING FROM ABOUT .20% TO ABUT .80%, AND HARDENING THE PREPARE COMPOSITION AT SUBSTANTIALLY THE SAME HARDENING TEMPERATURE EMPLOYED FOR HARDENING THE HIGH SPEED STEEL.
 10. A HARDENED ALLOY STEEL COMPOSITION CONSISTING ESSENTIALLY OF ABOUT .5% CARBON, ABOUT 2.0% TUNGSTEN, ABOUT 3.0% MOLYBDENUM, ABOUT 4.6% CHROMIUM, ABOUT 1.0% VANADIUM WITH THE REMAINDER SUBSTANTIALLY IRON, SAID COMPOSITION AFTER HARDENING CONSISTING ESSENTIALLY OF AN ESSENTIALLY MARTENSITIC STRUCTURE CONTAINING LESS THAN 5% UNDISSOLVED EXCESS CARBIDES HAVING A ROOM TEMPERATURE HARDENESS IN EXCESS OF ROCKWELL "C" 57 AND CHARACTERIZED BY A RATIO OF UNNOTCHED IMPACT TO HARDNESS IN EXCESS OF TWO TO ONE EXPRESSED IN UNITS OF FOOT-POUNDS TO ROCKWELL "C". 